Project 1: Time Domian Electron Paramagnetic Resonance Imaging:Summary: Low Field Imaging of Tumor Physiology.Sensitivity enhancement for improved spatial resolution: We have incorporated sensitive signal digitizer/ averager system to capture the weak MR signals from the contrast agent so that at significantly lower doses, it is possible to form images with mm3 resolution.Image data acquisition strategies to minimize image collection times: We have previously implemented Fourier Imaging strategies in EPR Imaging for the first time. This method unlike the commonly used filtered back projection methods significantly enhances the spatial resolution of the images. This strategy, while commonly used in conventional MRI is difficult to implement directly in EPRI. However, we developed a new approach where using static field gradients, we can use Fourier Imaging methods. This method, though compared to MRI, is time-inefficient. To minimize the data collection times, the image data collection procedure was evaluated critically. By incorporating changes in the signal data acquisition as well as managing the gradients, we have been able to minimize the overheads in time to collect images. Currently, it is possible to obtain a three-dimensional image data sets in under 5 minutes. Image reconstruction algorithms which can sensitively report on pO2 changes. Our prior reconstruction methods could form pO2 images with a precision of +/- 10 mm Hg in the range of 0 - 100 mm Hg. While in vivo oxygen ranges between 0-60 mm Hg in tissue, tumors display oxygen levels between 0-40 mm Hg and pO2 levels less than 10 mm Hg are considered radiobiologically hypoxic and display radioresistance. It is therefore necessary to identify such regions with precision in pO2 and useful spatial resolution. We have developed, tested and optimized image reconstruction methods which can reconstruct images with graphics user interface for general purpose users.Co-registration of pO2 images with anatomic images: As mentioned, EPRI is a low field MRI technique which can form images from the signals detected from a paramagnetic contrast agent. However, no anatomic information is available from EPRI. To provide anatomic overlay to the pO2 images of EPRI, we have designed and tested a resonator and gantry which can be used both in the EPRI and MRI at 7T. Since the operational RF frequency of EPRI at 10 mT and 7T is 300 MHz, we have constructed resonator coil which can be used in both modalities and also the associated gantry so that the object need be disturbed between the two scans and can be maintained under anesthesia during transport.